Patent GB-635370-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04M15/00
Filed: 1947-06-21
Abstract: 635,370. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., ISTERLING, J., and BEALE, C. E. June 21, 1947, No. 16436. [Class 40 (iv)] In a satellite exchange system, in which in order to permit the appropriate metering fee to be readily determined by discriminating selector repeaters in the satellite and subsatellite exchanges each exchange is designated by a characteristic combination of the first two digits, the designations of a satellite and its. associated sub-satellites have different third digits to enable a single group of junctions between the main and the satellite exchange to be used in common by the subsatellites, and in the main exchange equipment associated with each common junction responds to the third digit to control metering in respect of calls from the main exchange to the satellite or its associated sub-satellites and to prevent the setting up of a call should the third digit be inappropriate to the first 'two. The lay-out for an area comprising two main exchanges A, P is shown in Figs. 1, 2. Call from the main exchange A to a satellite B. On a main exchange subscriber SUB dialling the digits 36 characterising the satellite B, he is connected over corresponding levels of the first and second group selectors 1GS, 2GS and the path SLA to the metering control equipment CORS1 shown in detail in Figs. 3, 4. Closure of the incoming loop operates relays PA, A, the latter completing a circuit over a rectifier MRB and the impedance coil I for seizing the third group selector 3GS in the satellite B. Guard relay B pulls up, completes a holding circuit for PA and operates BR which shunts out the upper coil of relay PA. The third digit (1, 2, 3, 4) steps a uniselector U and is also repeated over the outgoing junction, relays C, CA being operative to connect a resistance YC across the loop to improve the re-transmission of the impulses. At the end of the digit, relay C releases followed by CA, and a circuit is completed for relay DC over the wiper U1 of the uniselector to earth. Operation of DC completes a self-holding circuit and prevents the succeeding digits acting on the magnet UM. The fourth and fifth digits set the final selector,at the satellite B. When the called subscriber replies, relay D is operated by reversal of current and relay DD follows to repeat back the reversal. The leads S, Z are connected to pulse-generating cam-controlled contacts, and the first S pulse after DD pulls up operates relay DA which holds. The subsequent Z pulse causes relay DB to operate and hold, thus completing a circuit from the metering pulse lead 11, corresponding to the path SLA, to the relay J. During the Z pulse, a number of metering pulses are fed into the lead 11, and are repeated by J over the private wire of the calling subscriber. At the end of the Z pulse DA releases. Should the third digit have been inappropriate to the wanted exchange, relay NU operates from earth in the uniselector U to disconnect the outgoing loop and to send number unobtainable tone to the calling subscriber. Calls from main exchange A to sub-satellites E, F. If the first two digits are 38 designating the sub-satellite E, the path SLC is seized and relay PC operates in the metering control equipment CORS1. Providing the third digit 7 or 8 is dialled, the subsequent operation is similar to that described above, except that the metering pulse lead 13 instead of lead 11 is utilised. Similarly if the digits 375 are dialled, a call is set up to the sub-satellite F over the path SLB, the metering lead 12 being utilized. Metering by duration. On the called subscriber replying, operation of relay D starts a timing device, which at three-minute intervals sends an audible warning to the calling subscriber and effects a switching operation to release DB by de-energizing its upper winding. The metering operation of relays DA, DB and J would then be repeated in a similar manner to that described above.